1. Field of the Invention
This invention relates to devices for processing offset-cum-signals such as video signals.
2. Description of the Related Art
In the still video apparatus, for example, the signal is processed so that the luminance signal and color signal are recorded in superimposed relation. In this case, the R-Y and B-Y signals as the color difference signals are recorded in the form of a line-sequence signal. In order to discriminate between the (R-Y) and (B-Y), signals, a DC offset for each line is added to this line-sequence signal.
For this reason, the still video apparatus necessitates a circuit for depriving the offset-contained color difference signals of the offset when during reproduction.
The mode of processing such color difference signals will be explained by reference to FIGS. 1a and 1b. FIG. 1a shows the reproduced signal of the still video apparatus, where the R-Y signal and the B-Y signal form the line-sequence signal having the offset. Such signal is converted to a line-sequence signal having no offset shown in FIG. 1b by passing it through a circuit performing offset removal.
In the past, such an offset removal has been realized by the circuit shown in FIG. 2.
In FIG. 2, the offset-cum-color difference line-sequence signal 1 such as that shown in FIG. 1a is applied to each of clamp circuits 2 and 3 which perform clamping during the horizontal blanking period. For example, 2 is made the clamp circuit for the R-Y signal, 3 is made the clamp circuit for the B-Y signal, and the potentials at the clamp points are made so as to be the same. Therefore, the blanking level of the R-Y signal produced from the clamp circuit 2 and the blanking level of the B-Y signal produced from the clamp circuit 3 become the same potential, and an offset-free color difference line-sequence signal 5 is obtained through a switching circuit 4 for changing over between the R-Y signal from the clamp circuit 2 and B-Y signal from the clamp circuit 3.
In such an offset removing circuit, however, the characteristics of the clamp circuit 2 and the clamp circuit 3 must be identical to each other. Otherwise, it would be difficult to assure removal of the offset. Also, adjustment for equalizing the characteristics of the clamp circuits must be made.